Effect of surfactant in an airway closure model

A model of the bronchioles lined by the airway surface liquid is employed to investi-gate the Plateau-Rayleigh instability that can lead to the occlusion of the airways. This physiologically relevant phenomenon is normally occurring in distal airways, i.e., in the bronchioles from the seventh generation on. Special attention is paid to the effect of surfactant dispersed in the liquid phase and along the liquid-gas interface. A single-layer Newtonian film is simulated in a rigid capillary pipe in order to isolate the impact of the surfactant and unravel their complex dynamics coupled with the multiphase liquid-gas dynamics. Apart from the primary instability leading to airway closure, we focus on the postcoalescence wall stresses and stress gradients produced by the bifrontal plug growth. With our model, we demonstrate that increasing the surfactant concentration and their strength, the airway closure slows and the wall stresses are reduced up to 20%. Within the physiological application intended for our model, we study the stability of the multiphase system. We predict the generation at which airway closure will occur depending on the liquid lining thickness and the initial surfactant concentration.